In her new movie
"The Lifeguard,"
Kristen Bell's character, on the verge of 30 years old, begins a sexual relationship with a 16-year-old boy. In a new interview, Bell talks about the graphic sex scene she filmed with her co-star, 19-year-old
David Lambert, and even sheds a little more light on the
"Veronica Mars" movie.

"We really shook hands and said, 'Let's make this graphic and real'," Bell tells
Vanity Fair. "Even prior to rolling, I think I just grabbed his hands and put them all over my chest and said, 'This is it. Don't be shy. Do what you do. I won't be uncomfortable. I trust you.'" She says Lambert was the picture of professionalism, adding, "There's a lot of choreography going into the camera work and making sure you can't see the, like, one inch of fabric that is actually keeping you from having sex." Sounds like it's going to be a pretty revealing scene.

What did her
fiance,
Dax Shepard, think of the intimate moment? Bell says she offered to let him read the script beforehand to see if he wanted to discuss it. "And he said, 'You know what, I don't care. I trust you. As long as you don't come back pregnant, I don't care.'" The ultimate irony, is she came back pregnant. Bell discovered while filming the movie that she was expecting her first baby with Shepard. Their daughter
Lincoln was born March 28.

As for the "Veronica Mars" movie, Bell calls the last day of shooting a "heartbreak." "I entered this relationship knowing that this would end," she says. "But it felt, still to the very last day when my car pulled out of the parking lot, so surreal. I thought, 'I cannot f***ing believe that we made the 'Veronica Mars' movie.'"

Bell admits making the movie was just as fun as the TV show, if not more. She says the cast even brought their kids to set so they could play together. Kristen also reveals how
Jamie Lee Curtis became involved in the movie. Fans were surprised to see Curtis pop up in the
teaser shown at Comic-Con, but Kristen says it was easy to get her on board. "We had done a movie together, and we get along gloriously," she explains. "I just texted her and asked her, and she literally responded, 'Where and when?' It was so exciting!"